Railroads have long sought a rapid, economical, and reliable method for determining which cars are part of a moving train. Usually, this requires that the train be stopped or slowed to a speed of less than approximately 8 miles per hour so that a trainman may read the serial numbers on the sides of the cars (accuracy decreases significantly at higher speeds). Travel time is lost with this procedure, but the economic incentive to know the location of each car (e.g., demurrage) is great. Therefore, this inefficient method is still the customary one.
Numerous mechanical systems that claim high accuracy even with trains moving at speeds of 50 miles per hour or more have been proposed and at least several dozen patented. Most of these, however, require placement of special coded labels or equipment on each car. (See, for example, U.S. Pat. Nos. 3,106,706, 3,316,392, 3,377,616, and 4,002,889.) Various factors, including the high cost of installing and maintaining these labels or equipment, have, for the most part, prevented the railroads from using any of these systems. One of these systems was employed commercially, but was later abandoned for several reasons, including insufficient accuracy.
A system that does not require special labels or equipment on the cars is disclosed in U.S. Pat. No. 2,956,117. In accordance with that disclosure, a television camera at track-side is linked to a television receiver at a remote location (for example, at the train yard). The video signal received is recorded on film, which is then processed for later viewing. An optical system compensates for the low speed and resolution of the video tube (image orthicon or vidicon) employed. (An image orthicon has a 20 percent lag; a vidicon typically has a 40 percent lag, although it could be as low as 20 percent.) Special circuitry and equipment move the film during recording at a speed proportional to the train's velocity past the camera.
U.S. Pat. No. 3,238,358 discloses an identification system using coded labels on the axles of the cars, the labels being applied by special equipment. An operator located at a distance from the labeling equipment views the serial number on each car by means of television equipment so that he can encode the serial number. (See column 6, line 3 et seq.)